High-speed MIR photodetectors with high sensitivity are needed for many applications, including MIR hyper-spectral imaging, biomedical sensing, environment monitoring, and astronomy. Yet, it remains a great challenge to realize sensitive and cost-effective MIR photodetectors with short response time (nanoseconds or picoseconds) at room temperature, especially in the longer wavelength range (>8 μm), due to the fundamental limitations in current detection technologies and their lack of compatibility with complementary metal-oxide-semiconductor (CMOS) circuits.